This invention is generally directed to thermographic machines for relief printing, and more particularly to a self contained recirculating powder and vacuuming assembly contained therein.
Presently, one element of a thermographic machine for relief printing is utilized to both deposit the thermographic powder atop paper stock which has been wet inked and is made to pass below a powder discharge tray by conveyor. Adjacent the powder discharge tray is a vacuum actuated powder pickup slot which removes loose, unadhered powder from atop the paper stock before it is passed on for heat fusion of the adhered powder.
The housing containing a blower and the powder tray typically is structured so as to discharge the powder and air out through an outlet into either atmosphere or into a collecting bag. This process results in an unacceptable discharge of the fine thermographic powder into the atmosphere.
One such thermographic machine is generally shown in U.S. Pat. No. 4,805,531 to Sarda which is particularly directed to a unique arrangement for cutting and manipulating paper stock. An anti-pollution grain dryer which includes a system for recycling air suction from the bin through an external cyclone dust separator back into a plenum chamber for reuse is disclosed in U.S. Pat. No. 4,241,517 to Carpenter.
The present system provides for a self contained recirculating powdering and vacuuming assembly which removes the loose powder from the inked paper stock more efficiently by the application of directed air toward the pickup slot from either side thereof and then recollects the loose powder and redeposits it into the powder tray for reuse. Thus, no powder ever exits the assembly but rather continues to be recycled therewithin until fully used or replenished.